1. Field of the Invention
The invention relates to immersion ultrasonic non-destructive evaluation within internally defined cavities of inanimate test objects, including in downwardly facing cavities by a test system and test methods that block the cavity opening so that ultrasonic immersion fluid remains in the cavity during the inspection procedure. Embodiments of the immersion ultrasound inspection system and test methods described herein are suitable for immersion inspection of test objects with inclined or vertical bottom opening cavities that otherwise are not capable of retaining ultrasonic testing immersion fluid. Embodiments of the methods and apparatus of the invention are suitable for in situ inspection of steam turbine engine steam inlets, including steam inlet sleeve necks, while the steam inlet remains in situ within a steam turbine upper housing.
2. Description of the Prior Art
FIG. 1 shows a known High Pressure (HP) and HP/Intermediate Pressure (IP) steam turbine engine 8, having a rotating rotor 9 that includes a row of turbine blades 10. The turbine engine 8 has an upper housing 11 that includes a plurality of steam inlets 12. An inlet sleeve 14 used in the steam turbine directs steam from the inlet and its piping, 12, including the elbow portion 13, through the outer and inner cylinder walls of the upper housing 11. The steam inlet sleeve downstream outlet portion 16 adjoins a nozzle chamber for directing the pressurized steam onto the turbine blades 10. As shown in greater detail in FIGS. 2 and 3, the inlet sleeve 14 is essentially a cantilevered tubular structure fixed at the upstream inlet sleeve neck 18 adjoining the elbow portion 13, while the outlet portion 16 is only restrained by a friction interlocked sealing device proximal the nozzle chamber/turbine blades 10. Steam flow in the steam inlet structure 12 can induce vibration in the inlet sleeve 14, especially if there is a loss of frictional damping between the sleeve and the sealing device. Either constant or intermittent vibration of the sleeve 14 can result in a fatigue crack at the trepan fillet radius of the inlet sleeve neck 18. These fatigue cracks, if undetected, can result in a through wall failure of the sleeve 14 and eventually force the unit out of service.
Frequent NDE inspection and early detection is required to preclude such events. For that reason, the sleeves are inspected periodically during scheduled maintenance service outages and replaced if cracks are present. During inspection the steam turbine engine 10 upper housing is removed and elevated on a service pad, so that inspectors can insert NDE inspection instruments into the upwardly facing inlet sleeve downstream outlets 16 of the steam inlet sleeves 14. The sleeve necks 18 are inspected by inserting NDE test instruments up the inclined vertically oriented steam sleeves 14. Known ultrasonic inspection methods for steam inlet sleeve neck 18 NDE involve cleaning the inner surface of the generally tubular steam sleeve proximal the sleeve neck 18 and performing contact-type ultrasonic inspection of the neck structure by directing ultrasonic waves through the neck with either single angle or phased array transducers that are oriented relative to the neck with ultrasonically transparent orientation wedges. It is difficult and inconvenient to clean the steam sleeve 14 internal surfaces, align transducer orientation wedges at an extended distance upstream the sleeve 14 and then maneuver the wedges and transducer probe to capture a satisfactory inspection image. Also surface texture or physical condition of some cavities makes them difficult to establish satisfactory direct contact with the transducer orientation wedge that is necessary to obtain a satisfactory inspection image.